[lti] Reset all flags properly with potential exceptions considered

Summary:
I found that sometimes we are not correctly reseting synthesis mode flag back to false, which is caused by not handling exceptions and rethrow it after we reset the flag.

I still haven't figured out why we are throwing exceptions during synthesis mode that are not caught lower in the stack, but it's always better to be safe.

Since I'm already here, I also made similar changes for all other flags.

Changelog: [internal]

Reviewed By: mvitousek

Differential Revision: D41361086

fbshipit-source-id: 6fa4b9b2dd4b26a30c41196c1f82b9f7773432bc

src/typing/context.ml

@@ -805,9 +805,9 @@ let run_in_implicit_instantiation_mode cx f =
 let run_in_post_inference_mode cx f =
   let saved = cx.phase in
   cx.phase <- PostInference;
-  let result = f () in
+  let result = Base.Result.try_with f in
   cx.phase <- saved;
-  result
+  Base.Result.ok_exn result
 
 let set_trust_graph cx trust_graph = cx.ccx.sig_cx <- { cx.ccx.sig_cx with trust_graph }
 
@@ -836,15 +836,9 @@ let set_environment cx env = cx.environment <- env
 let run_in_hint_decomp cx f =
   let old = cx.in_hint_decomp in
   cx.in_hint_decomp <- true;
-  let exn =
-    try
-      f ();
-      None
-    with
-    | exn -> Some exn
-  in
+  let result = Base.Result.try_with f in
   cx.in_hint_decomp <- old;
-  Base.Option.iter exn ~f:raise
+  Base.Result.ok_exn result
 
 let run_and_rolled_back_cache cx f =
   let saved_constraint_cache = !(cx.ccx.constraint_cache) in
@@ -855,7 +849,7 @@ let run_and_rolled_back_cache cx f =
   let saved_eval_repos_cache = !(cx.ccx.eval_repos_cache) in
   let saved_fix_cache = !(cx.ccx.fix_cache) in
   let saved_spread_cache = !(cx.ccx.spread_cache) in
-  let result = f () in
+  let result = Base.Result.try_with f in
   cx.ccx.constraint_cache := saved_constraint_cache;
   cx.ccx.subst_cache := saved_subst_cache;
   cx.ccx.repos_cache := saved_repos_cache;
@@ -864,18 +858,18 @@ let run_and_rolled_back_cache cx f =
   cx.ccx.eval_repos_cache := saved_eval_repos_cache;
   cx.ccx.fix_cache := saved_fix_cache;
   cx.ccx.spread_cache := saved_spread_cache;
-  result
+  Base.Result.ok_exn result
 
 let run_in_synthesis_mode cx f =
   let old_synthesis_mode = cx.in_synthesis_mode in
   let old_produced_placeholders = cx.ccx.produced_placeholders in
   cx.ccx.produced_placeholders <- false;
   cx.in_synthesis_mode <- true;
-  let result = run_and_rolled_back_cache cx f in
+  let result = Base.Result.try_with f in
   cx.in_synthesis_mode <- old_synthesis_mode;
   let produced_placeholders = cx.ccx.produced_placeholders in
   cx.ccx.produced_placeholders <- old_produced_placeholders;
-  (produced_placeholders, result)
+  (produced_placeholders, Base.Result.ok_exn result)
 
 (* Given a sig context, it makes sense to clear the parts that are shared with
    the master sig context. Why? The master sig context, which contains global